Pick GLM 5.1 for long-horizon autonomous agentic engineering (up to 8-hour runs) or state-of-the-art open-weight coding (topped swe-bench pro at launch). Pick Grok Code Fast 1 for fast, cheap agentic coding at $0.20/$1.50 or low-latency code generation and terminal tasks. Choose GLM 5.1 if you need self-hosting or data privacy; Grok Code Fast 1 if you want a managed API.
GLM 5.1 (Z.ai, China) and Grok Code Fast 1 (xAI, US) line up two different AI ecosystems against each other — a comparison that is as much about cost philosophy and openness as raw capability. GLM 5.1 is an open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours. Grok Code Fast 1 is xAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. They diverge most on price, context window and open vs. closed weights — each quantified below from the models' real specs.
Key differences
Price: Grok Code Fast 1 is about 7× cheaper on input ($0.2/$1.5 per 1M tokens vs $1.4/$4.4 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
Context window: Grok Code Fast 1 holds 1.3× more — 256K (~384 pages) vs 200K (~300 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
Recency: GLM 5.1 is the newer model by about 7 months (released April 7, 2026), usually meaning fresher training data and capabilities.
Ecosystem: this is a China-vs-US matchup — they differ in pricing philosophy, data-residency options, and tooling ecosystems, not only benchmarks.
Specifications
Spec
GLM 5.1
Grok Code Fast 1
Provider
Z.ai (China)
xAI (US)
Released
April 7, 2026
August 28, 2025
Context window
200K (~300 pages)
256K (~384 pages)
Price (in/out)
$1.4/$4.4 per 1M tokens
$0.2/$1.5 per 1M tokens
Open weight?
Yes — self-hostable
No — API only
Modalities
text, code
text, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Long-horizon autonomous agentic engineering (up to 8-hour runs): GLM 5.1 — An open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours — and its weights are open while Grok Code Fast 1 is API-only.
State-of-the-art open-weight coding (topped SWE-Bench Pro at launch): GLM 5.1 — Open weights make this possible at all — Grok Code Fast 1 is API-only, so it cannot leave the vendor's servers.
Sustained tool use across thousands of calls: GLM 5.1 — An open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours — and it is the newer of the two.
Fast, cheap agentic coding at $0.20/$1.50: Grok Code Fast 1 — At $0.2/$1.5 per 1M tokens it undercuts GLM 5.1 ($1.4/$4.4 per 1M tokens), and that gap compounds at volume.
Low-latency code generation and terminal tasks: Grok Code Fast 1 — XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality — and it runs cheaper at $0.2/$1.5 per 1M tokens.
High-volume coding pipelines where speed beats peak quality: Grok Code Fast 1 — XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality — and it carries the larger 256K context.
Lowest cost at scale: Grok Code Fast 1 — At $0.2/$1.5 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input: Grok Code Fast 1 — Its 256K window is about 1.3× larger than GLM 5.1's 200K, fitting roughly 384 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume: Grok Code Fast 1 — At $0.2/$1.5 per 1M tokens it undercuts GLM 5.1, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases: Grok Code Fast 1 — Larger 256K window fits more in one prompt.
A team with data-privacy or self-hosting needs: GLM 5.1 — Open weights let you run it on your own hardware; Grok Code Fast 1 is API-only.
Anyone whose priority is long-horizon autonomous agentic engineering (up to 8-hour runs): GLM 5.1 — It is specifically built for that.
Anyone whose priority is fast, cheap agentic coding at $0.20/$1.50: Grok Code Fast 1 — That is its strongest area.
An enterprise with regional data-residency rules: Grok Code Fast 1 or GLM 5.1 — Origin (China vs US) affects where data is processed and which compliance regime applies — check the provider's terms for your region.
GLM 5.1: where it fits
An open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours. Released April 7, 2026 by Z.ai, it is built for long-horizon autonomous agentic engineering (up to 8-hour runs), state-of-the-art open-weight coding (topped SWE-Bench Pro at launch), sustained tool use across thousands of calls, and self-hostable under a permissive MIT license.
Its trade-offs are real: text-only, with no image, audio, or video input, and 754B-parameter MoE demands heavy GPU resources to self-host. At $1.4 in / $4.4 out per million tokens, it sits in the mid price band.
Grok Code Fast 1: where it fits
XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. Released August 28, 2025 by xAI, it is built for fast, cheap agentic coding at $0.20/$1.50, low-latency code generation and terminal tasks, high-volume coding pipelines where speed beats peak quality, and a 256K window sized for real codebases.
Its trade-offs: text and code only — no image, audio or video input, xAI did not publish a SWE-Bench Verified score, a speed-tier coding model, not a frontier reasoner, and narrow focus — built for code, not general knowledge work. At $0.2 in / $1.5 out per million tokens, it sits in the budget price band.
The bottom line for this matchup
The defining split here is open vs. closed. GLM 5.1 gives you weights you control — self-host it, fine-tune it, keep data in-house, pay only for hardware. Grok Code Fast 1 gives you a managed, always-updated API with no infrastructure to run. Teams with GPUs, privacy requirements, or huge volume often favour the open model; teams that want zero ops and the latest capabilities favour the closed one. Capability is close enough that this operational question, not the benchmark, usually decides it.
Frequently asked questions
Is GLM 5.1 or Grok Code Fast 1 better for coding?
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, GLM 5.1 leans toward long-horizon autonomous agentic engineering (up to 8-hour runs) while Grok Code Fast 1 leans toward fast, cheap agentic coding at $0.20/$1.50, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, GLM 5.1 or Grok Code Fast 1?
GLM 5.1 is open-weight, so self-hosting means no per-token fee (you pay for hardware instead), while Grok Code Fast 1 is API-metered at $0.2/$1.5 per 1M tokens. For most teams without GPUs, the API model is cheaper to start; at very high volume, self-hosting can win.
Which has the bigger context window?
Grok Code Fast 1 — 256K vs 200K, about 1.3× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both GLM 5.1 and Grok Code Fast 1 together?
Yes — a multi-model platform like LumiChats gives you GLM 5.1, Grok Code Fast 1 and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, GLM 5.1 or Grok Code Fast 1?
GLM 5.1 — released April 7, 2026, about 7 months after Grok Code Fast 1.
GLM 5.1 vs Grok Code Fast 1
Z.ai · China | xAI · US · Updated June 2026
Quick verdict
Pick GLM 5.1 for long-horizon autonomous agentic engineering (up to 8-hour runs) or state-of-the-art open-weight coding (topped swe-bench pro at launch). Pick Grok Code Fast 1 for fast, cheap agentic coding at $0.20/$1.50 or low-latency code generation and terminal tasks. Choose GLM 5.1 if you need self-hosting or data privacy; Grok Code Fast 1 if you want a managed API.
GLM 5.1 (Z.ai, China) and Grok Code Fast 1 (xAI, US) line up two different AI ecosystems against each other — a comparison that is as much about cost philosophy and openness as raw capability. GLM 5.1 is an open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours. Grok Code Fast 1 is xAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. They diverge most on price, context window and open vs. closed weights — each quantified below from the models' real specs.
Key differences at a glance
▸Price: Grok Code Fast 1 is about 7× cheaper on input ($0.2/$1.5 per 1M tokens vs $1.4/$4.4 per 1M tokens) — a large enough gap that at scale it can be the single biggest line item in the decision.
▸Context window: Grok Code Fast 1 holds 1.3× more — 256K (~384 pages) vs 200K (~300 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
▸Recency: GLM 5.1 is the newer model by about 7 months (released April 7, 2026), usually meaning fresher training data and capabilities.
▸Ecosystem: this is a China-vs-US matchup — they differ in pricing philosophy, data-residency options, and tooling ecosystems, not only benchmarks.
Side-by-side specs
Spec
GLM 5.1
Grok Code Fast 1
Provider
Z.ai (China)
xAI (US)
Released
April 7, 2026
August 28, 2025
Context window
200K (~300 pages)
256K (~384 pages)
Price (in/out)
$1.4/$4.4 per 1M tokens
$0.2/$1.5 per 1M tokens
Open weight?
Yes — self-hostable
No — API only
Modalities
text, code
text, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
Long-horizon autonomous agentic engineering (up to 8-hour runs)
GLM 5.1
An open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours — and its weights are open while Grok Code Fast 1 is API-only.
State-of-the-art open-weight coding (topped SWE-Bench Pro at launch)
GLM 5.1
Open weights make this possible at all — Grok Code Fast 1 is API-only, so it cannot leave the vendor's servers.
Sustained tool use across thousands of calls
GLM 5.1
An open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours — and it is the newer of the two.
Fast, cheap agentic coding at $0.20/$1.50
Grok Code Fast 1
At $0.2/$1.5 per 1M tokens it undercuts GLM 5.1 ($1.4/$4.4 per 1M tokens), and that gap compounds at volume.
Low-latency code generation and terminal tasks
Grok Code Fast 1
XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality — and it runs cheaper at $0.2/$1.5 per 1M tokens.
High-volume coding pipelines where speed beats peak quality
Grok Code Fast 1
XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality — and it carries the larger 256K context.
Lowest cost at scale
Grok Code Fast 1
At $0.2/$1.5 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Largest single-prompt input
Grok Code Fast 1
Its 256K window is about 1.3× larger than GLM 5.1's 200K, fitting roughly 384 pages in one prompt.
Which should you pick?
A cost-sensitive startup shipping high volume
→ Grok Code Fast 1
At $0.2/$1.5 per 1M tokens it undercuts GLM 5.1, and on millions of tokens that margin decides the monthly bill.
Someone analysing very long documents or codebases
→ Grok Code Fast 1
Larger 256K window fits more in one prompt.
A team with data-privacy or self-hosting needs
→ GLM 5.1
Open weights let you run it on your own hardware; Grok Code Fast 1 is API-only.
Anyone whose priority is long-horizon autonomous agentic engineering (up to 8-hour runs)
→ GLM 5.1
It is specifically built for that.
Anyone whose priority is fast, cheap agentic coding at $0.20/$1.50
→ Grok Code Fast 1
That is its strongest area.
An enterprise with regional data-residency rules
→ Grok Code Fast 1 or GLM 5.1
Origin (China vs US) affects where data is processed and which compliance regime applies — check the provider's terms for your region.
GLM 5.1: where it fits
An open-weight (MIT) Chinese coding model built for long-horizon agentic engineering, topping SWE-Bench Pro at launch while running autonomously for up to 8 hours. Released April 7, 2026 by Z.ai, it is built for long-horizon autonomous agentic engineering (up to 8-hour runs), state-of-the-art open-weight coding (topped SWE-Bench Pro at launch), sustained tool use across thousands of calls, and self-hostable under a permissive MIT license.
Its trade-offs are real: text-only, with no image, audio, or video input, and 754B-parameter MoE demands heavy GPU resources to self-host. At $1.4 in / $4.4 out per million tokens, it sits in the mid price band.
Grok Code Fast 1: where it fits
XAI's speed-tier coding model at $0.20/$1.50 with a 256K window — cheap, fast agentic code over frontier quality. Released August 28, 2025 by xAI, it is built for fast, cheap agentic coding at $0.20/$1.50, low-latency code generation and terminal tasks, high-volume coding pipelines where speed beats peak quality, and a 256K window sized for real codebases.
Its trade-offs: text and code only — no image, audio or video input, xAI did not publish a SWE-Bench Verified score, a speed-tier coding model, not a frontier reasoner, and narrow focus — built for code, not general knowledge work. At $0.2 in / $1.5 out per million tokens, it sits in the budget price band.
The bottom line for this matchup
The defining split here is open vs. closed. GLM 5.1 gives you weights you control — self-host it, fine-tune it, keep data in-house, pay only for hardware. Grok Code Fast 1 gives you a managed, always-updated API with no infrastructure to run. Teams with GPUs, privacy requirements, or huge volume often favour the open model; teams that want zero ops and the latest capabilities favour the closed one. Capability is close enough that this operational question, not the benchmark, usually decides it.
Want both GLM 5.1 and Grok Code Fast 1 without two subscriptions? LumiChats gives you these plus 40+ models under one ₹69/day pass (about $1/day) — draft with one, cross-check with the other.
Public SWE-Bench figures are not available for either model, so the honest test is your own repository — run an identical real bug through both. By design, GLM 5.1 leans toward long-horizon autonomous agentic engineering (up to 8-hour runs) while Grok Code Fast 1 leans toward fast, cheap agentic coding at $0.20/$1.50, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, GLM 5.1 or Grok Code Fast 1?
GLM 5.1 is open-weight, so self-hosting means no per-token fee (you pay for hardware instead), while Grok Code Fast 1 is API-metered at $0.2/$1.5 per 1M tokens. For most teams without GPUs, the API model is cheaper to start; at very high volume, self-hosting can win.
Which has the bigger context window?
Grok Code Fast 1 — 256K vs 200K, about 1.3× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both GLM 5.1 and Grok Code Fast 1 together?
Yes — a multi-model platform like LumiChats gives you GLM 5.1, Grok Code Fast 1 and 40+ others under one ₹69/day pass (about $1/day), so you can draft with one and cross-check with the other instead of buying two subscriptions.
Which is newer, GLM 5.1 or Grok Code Fast 1?
GLM 5.1 — released April 7, 2026, about 7 months after Grok Code Fast 1.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.