Claude Sonnet 5.5 vs Gemini 3.5 Flash
Anthropic · US | Google · US · Updated June 2026
Quick verdict
Pick Claude Sonnet 5.5 for terminal-bench 4.0 agentic coding jumps to 70.6%, up from claude sonnet 5's 10.3% or same $2/$10 per million token pricing as sonnet 5, with cache-read price cut 50% to $0.10/mtok as of october 7, 2026. Pick Gemini 3.5 Flash for speed — roughly 4x faster than rivals or cost — about a third the price. On a tight budget at scale, Gemini 3.5 Flash is the value pick.
Claude Sonnet 5.5 (Anthropic) and Gemini 3.5 Flash (Google) are two of the models people most often weigh against each other in 2026. Claude Sonnet 5.5 is anthropic's September 28, 2026 mid-tier update — same $2/$10 pricing as Sonnet 5 but a large agentic-coding jump (Terminal-Bench 4.0: 70.6% vs 10.3%). Gemini 3.5 Flash is google's fast, cheap class that now beats last year's premium Pro — the value-and-reach play. Their biggest split is price, and the breakdown below shows exactly how that plays out for your workload.
Key differences at a glance
- ▸Price: Gemini 3.5 Flash is about 1.3× cheaper on input ($1.5/$9 per 1M tokens vs $2/$10 per 1M tokens) — modest, but it adds up at steady volume.
- ▸Context window: both advertise 1M tokens (~1,500 pages). Tie on paper — test on your own long inputs, since usable recall varies by model.
- ▸Recency: Claude Sonnet 5.5 is the newer model by about 4 months (released September 28, 2026), usually meaning fresher training data and capabilities.
Side-by-side specs
| Spec | Claude Sonnet 5.5 | Gemini 3.5 Flash |
|---|---|---|
| Provider | Anthropic (US) | Google (US) |
| Released | September 28, 2026 | May 19, 2026 |
| Context window | 1M tokens (~1,500 pages) | 1M (~1,500 pages) |
| Price (in/out) | $2/$10 per 1M tokens | $1.5/$9 per 1M tokens |
| Open weight? | No — API only | No — API only |
| Modalities | text, image, code | text, image, audio, video, code |
| SWE-Bench Verified | Not published | Not published |
| MRCR v2 @ 1M | Not published | Not published |
Who wins what
Terminal-Bench 4.0 agentic coding jumps to 70.6%, up from Claude Sonnet 5's 10.3%
Claude Sonnet 5.5
Anthropic's September 28, 2026 mid-tier update — same $2/$10 pricing as Sonnet 5 but a large agentic-coding jump (Terminal-Bench 4.0: 70.6% vs 10.3%) — and it is the newer of the two.
Same $2/$10 per million token pricing as Sonnet 5, with cache-read price cut 50% to $0.10/MTok as of October 7, 2026
Claude Sonnet 5.5
Claude Sonnet 5.5 lists same $2/$10 per million token pricing as Sonnet 5, with cache-read price cut 50% to $0.10/MTok as of October 7, 2026 among its strengths; Gemini 3.5 Flash does not.
Scores close to Opus 5.5 on several benchmarks (e.g. GDPval-AA v2.1 knowledge-work Elo) at a fraction of the cost
Claude Sonnet 5.5
Claude Sonnet 5.5 lists scores close to Opus 5.5 on several benchmarks (e.g. GDPval-AA v2.1 knowledge-work Elo) at a fraction of the cost among its strengths; Gemini 3.5 Flash does not.
Speed — roughly 4x faster than rivals
Gemini 3.5 Flash
Google's fast, cheap class that now beats last year's premium Pro — the value-and-reach play — and it runs cheaper at $1.5/$9 per 1M tokens.
Cost — about a third the price
Gemini 3.5 Flash
At $1.5/$9 per 1M tokens it undercuts Claude Sonnet 5.5 ($2/$10 per 1M tokens), and that gap compounds at volume.
Default in the Gemini app and Search AI Mode
Gemini 3.5 Flash
Gemini 3.5 Flash lists default in the Gemini app and Search AI Mode among its strengths; Claude Sonnet 5.5 does not.
Lowest cost at scale
Gemini 3.5 Flash
At $1.5/$9 per 1M tokens, it is the cheaper of the two — the gap dominates the bill on high-volume workloads.
Which should you pick?
A cost-sensitive startup shipping high volume
→ Gemini 3.5 Flash
At $1.5/$9 per 1M tokens it undercuts Claude Sonnet 5.5, and on millions of tokens that margin decides the monthly bill.
Anyone whose priority is terminal-bench 4.0 agentic coding jumps to 70.6%, up from claude sonnet 5's 10.3%
→ Claude Sonnet 5.5
It is specifically built for that.
Anyone whose priority is speed — roughly 4x faster than rivals
→ Gemini 3.5 Flash
That is its strongest area.
Claude Sonnet 5.5: where it fits
Anthropic's September 28, 2026 mid-tier update — same $2/$10 pricing as Sonnet 5 but a large agentic-coding jump (Terminal-Bench 4.0: 70.6% vs 10.3%). Released September 28, 2026 by Anthropic, it is built for terminal-Bench 4.0 agentic coding jumps to 70.6%, up from Claude Sonnet 5's 10.3%, same $2/$10 per million token pricing as Sonnet 5, with cache-read price cut 50% to $0.10/MTok as of October 7, 2026, scores close to Opus 5.5 on several benchmarks (e.g. GDPval-AA v2.1 knowledge-work Elo) at a fraction of the cost, and anthropic highlights stronger document/slide generation, spreadsheet work, and visual chart recognition (Chartography: 61.6%).
Its trade-offs are real: anthropic is explicit that Opus 5.5 'remains clearly stronger' on complex, open-ended work requiring sustained judgment, 1M-token context isn't uniformly available across every platform/plan, consistent with the rest of the 5.5 family, and mid-tier update released a week after Opus 5.5 (Sept 22) — Haiku 5.5 followed Oct 7 to complete the family. At $2 in / $10 out per million tokens, it sits in the mid price band.
Gemini 3.5 Flash: where it fits
Google's fast, cheap class that now beats last year's premium Pro — the value-and-reach play. Released May 19, 2026 by Google, it is built for speed — roughly 4x faster than rivals, cost — about a third the price, default in the Gemini app and Search AI Mode, and high-volume multimodal work.
Its trade-offs: flash tier, not the deepest reasoning, and pro-tier 3.5 held back at launch. At $1.5 in / $9 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Claude Sonnet 5.5 and Gemini 3.5 Flash overlap enough that the right pick depends on your specific job. Gemini 3.5 Flash costs less per token; and each leads in its own area — Claude Sonnet 5.5 for terminal-bench 4.0 agentic coding jumps to 70.6%, up from claude sonnet 5's 10.3%, Gemini 3.5 Flash for speed — roughly 4x faster than rivals. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both Claude Sonnet 5.5 and Gemini 3.5 Flash 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.
See pricingFrequently asked questions
Is Claude Sonnet 5.5 or Gemini 3.5 Flash 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, Claude Sonnet 5.5 leans toward terminal-bench 4.0 agentic coding jumps to 70.6%, up from claude sonnet 5's 10.3% while Gemini 3.5 Flash leans toward speed — roughly 4x faster than rivals, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Claude Sonnet 5.5 or Gemini 3.5 Flash?
Gemini 3.5 Flash is cheaper — $2/$10 per 1M tokens vs $1.5/$9 per 1M tokens, roughly 1.3× apart on input.
Which has the bigger context window?
Both advertise 1M tokens (~1,500 pages). Remember advertised ≠ usable: recall typically degrades before the ceiling.
Can I use both Claude Sonnet 5.5 and Gemini 3.5 Flash together?
Yes — a multi-model platform like LumiChats gives you Claude Sonnet 5.5, Gemini 3.5 Flash 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, Claude Sonnet 5.5 or Gemini 3.5 Flash?
Claude Sonnet 5.5 — released September 28, 2026, about 4 months after Gemini 3.5 Flash.
Related comparisons
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.