Pick Gemini 2.5 Pro for 1m context via api or strong multimodal reasoning. Pick GPT-5.1 for adaptive reasoning that scales compute to task difficulty or general-purpose reasoning, coding and tool use.
Gemini 2.5 Pro (Google) and GPT-5.1 (OpenAI) are two of the models people most often weigh against each other in 2026. Gemini 2.5 Pro is google's previous-gen 2M flagship — still a strong long-context multimodal option. GPT-5.1 is openAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. Their biggest split is context window, and the breakdown below shows exactly how that plays out for your workload.
Key differences
Context window: Gemini 2.5 Pro holds 2.5× more — 1M (~1,500 pages) vs 400K (~600 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
Recency: GPT-5.1 is the newer model by about 6 months (released November 13, 2025), usually meaning fresher training data and capabilities.
Specifications
Spec
Gemini 2.5 Pro
GPT-5.1
Provider
Google (US)
OpenAI (US)
Released
June 2025
November 13, 2025
Context window
1M (~1,500 pages)
400K (~600 pages)
Price (in/out)
$1.25/$10 per 1M tokens
$1.25/$10 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, audio, video, code
text, image, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
1M context via API: Gemini 2.5 Pro — Its 1M window holds about 2.5× more than GPT-5.1's 400K in a single prompt.
Strong multimodal reasoning: Gemini 2.5 Pro — Google's previous-gen 2M flagship — still a strong long-context multimodal option — and it carries the larger 1M context.
Science and maths benchmarks: Gemini 2.5 Pro — Gemini 2.5 Pro lists science and maths benchmarks among its strengths; GPT-5.1 does not.
Adaptive reasoning that scales compute to task difficulty: GPT-5.1 — OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line — and it is the newer of the two.
General-purpose reasoning, coding and tool use: GPT-5.1 — GPT-5.1 lists general-purpose reasoning, coding and tool use among its strengths; Gemini 2.5 Pro does not.
A large ~400K context for long documents and sessions: GPT-5.1 — GPT-5.1 lists a large ~400K context for long documents and sessions among its strengths; Gemini 2.5 Pro does not.
Largest single-prompt input: Gemini 2.5 Pro — Its 1M window is about 2.5× larger than GPT-5.1's 400K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
Someone analysing very long documents or codebases: Gemini 2.5 Pro — Larger 1M window fits more in one prompt.
Anyone whose priority is 1m context via api: Gemini 2.5 Pro — It is specifically built for that.
Anyone whose priority is adaptive reasoning that scales compute to task difficulty: GPT-5.1 — That is its strongest area.
Gemini 2.5 Pro: where it fits
Google's previous-gen 2M flagship — still a strong long-context multimodal option. Released June 2025 by Google, it is built for 1M context via API, strong multimodal reasoning, science and maths benchmarks, and whole-book and video analysis.
Its trade-offs are real: superseded by 3.x for newest features, and recall degrades on very long inputs. At $1.25 in / $10 out per million tokens, it sits in the mid price band.
GPT-5.1: where it fits
OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. Released November 13, 2025 by OpenAI, it is built for adaptive reasoning that scales compute to task difficulty, general-purpose reasoning, coding and tool use, a large ~400K context for long documents and sessions, and text and image input.
Its trade-offs: superseded by GPT-5.2 through GPT-5.6 — kept for compatibility rather than being current, no reliably published SWE-Bench Verified figure, exact context window unconfirmed (400K vs 410K across trackers), and premium output price at $10/1M for a now-older model. At $1.25 in / $10 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Gemini 2.5 Pro and GPT-5.1 overlap enough that the right pick depends on your specific job. Gemini 2.5 Pro holds the larger context; and each leads in its own area — Gemini 2.5 Pro for 1m context via api, GPT-5.1 for adaptive reasoning that scales compute to task difficulty. Rather than crowning one, run the same hard task through both once and let the results decide.
Frequently asked questions
Is Gemini 2.5 Pro or GPT-5.1 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, Gemini 2.5 Pro leans toward 1m context via api while GPT-5.1 leans toward adaptive reasoning that scales compute to task difficulty, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Gemini 2.5 Pro or GPT-5.1?
They are priced almost identically, so cost will not decide between them.
Which has the bigger context window?
Gemini 2.5 Pro — 1M vs 400K, about 2.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Gemini 2.5 Pro and GPT-5.1 together?
Yes — a multi-model platform like LumiChats gives you Gemini 2.5 Pro, GPT-5.1 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, Gemini 2.5 Pro or GPT-5.1?
GPT-5.1 — released November 13, 2025, about 6 months after Gemini 2.5 Pro.
Gemini 2.5 Pro vs GPT-5.1
Google · US | OpenAI · US · Updated June 2026
Quick verdict
Pick Gemini 2.5 Pro for 1m context via api or strong multimodal reasoning. Pick GPT-5.1 for adaptive reasoning that scales compute to task difficulty or general-purpose reasoning, coding and tool use.
Gemini 2.5 Pro (Google) and GPT-5.1 (OpenAI) are two of the models people most often weigh against each other in 2026. Gemini 2.5 Pro is google's previous-gen 2M flagship — still a strong long-context multimodal option. GPT-5.1 is openAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. Their biggest split is context window, and the breakdown below shows exactly how that plays out for your workload.
Key differences at a glance
▸Context window: Gemini 2.5 Pro holds 2.5× more — 1M (~1,500 pages) vs 400K (~600 pages). But effective recall usually fades long before the advertised ceiling, so the bigger number only helps if the model reasons over it.
▸Recency: GPT-5.1 is the newer model by about 6 months (released November 13, 2025), usually meaning fresher training data and capabilities.
Side-by-side specs
Spec
Gemini 2.5 Pro
GPT-5.1
Provider
Google (US)
OpenAI (US)
Released
June 2025
November 13, 2025
Context window
1M (~1,500 pages)
400K (~600 pages)
Price (in/out)
$1.25/$10 per 1M tokens
$1.25/$10 per 1M tokens
Open weight?
No — API only
No — API only
Modalities
text, image, audio, video, code
text, image, code
SWE-Bench Verified
Not published
Not published
MRCR v2 @ 1M
Not published
Not published
Who wins what
1M context via API
Gemini 2.5 Pro
Its 1M window holds about 2.5× more than GPT-5.1's 400K in a single prompt.
Strong multimodal reasoning
Gemini 2.5 Pro
Google's previous-gen 2M flagship — still a strong long-context multimodal option — and it carries the larger 1M context.
Science and maths benchmarks
Gemini 2.5 Pro
Gemini 2.5 Pro lists science and maths benchmarks among its strengths; GPT-5.1 does not.
Adaptive reasoning that scales compute to task difficulty
GPT-5.1
OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line — and it is the newer of the two.
General-purpose reasoning, coding and tool use
GPT-5.1
GPT-5.1 lists general-purpose reasoning, coding and tool use among its strengths; Gemini 2.5 Pro does not.
A large ~400K context for long documents and sessions
GPT-5.1
GPT-5.1 lists a large ~400K context for long documents and sessions among its strengths; Gemini 2.5 Pro does not.
Largest single-prompt input
Gemini 2.5 Pro
Its 1M window is about 2.5× larger than GPT-5.1's 400K, fitting roughly 1,500 pages in one prompt.
Which should you pick?
Someone analysing very long documents or codebases
→ Gemini 2.5 Pro
Larger 1M window fits more in one prompt.
Anyone whose priority is 1m context via api
→ Gemini 2.5 Pro
It is specifically built for that.
Anyone whose priority is adaptive reasoning that scales compute to task difficulty
→ GPT-5.1
That is its strongest area.
Gemini 2.5 Pro: where it fits
Google's previous-gen 2M flagship — still a strong long-context multimodal option. Released June 2025 by Google, it is built for 1M context via API, strong multimodal reasoning, science and maths benchmarks, and whole-book and video analysis.
Its trade-offs are real: superseded by 3.x for newest features, and recall degrades on very long inputs. At $1.25 in / $10 out per million tokens, it sits in the mid price band.
GPT-5.1: where it fits
OpenAI's late-2025 GPT-5.1 at $1.25/$10 — a capable general model since surpassed by the GPT-5.2–5.6 line. Released November 13, 2025 by OpenAI, it is built for adaptive reasoning that scales compute to task difficulty, general-purpose reasoning, coding and tool use, a large ~400K context for long documents and sessions, and text and image input.
Its trade-offs: superseded by GPT-5.2 through GPT-5.6 — kept for compatibility rather than being current, no reliably published SWE-Bench Verified figure, exact context window unconfirmed (400K vs 410K across trackers), and premium output price at $10/1M for a now-older model. At $1.25 in / $10 out per million tokens, it sits in the mid price band.
The bottom line for this matchup
Gemini 2.5 Pro and GPT-5.1 overlap enough that the right pick depends on your specific job. Gemini 2.5 Pro holds the larger context; and each leads in its own area — Gemini 2.5 Pro for 1m context via api, GPT-5.1 for adaptive reasoning that scales compute to task difficulty. Rather than crowning one, run the same hard task through both once and let the results decide.
Want both Gemini 2.5 Pro and GPT-5.1 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, Gemini 2.5 Pro leans toward 1m context via api while GPT-5.1 leans toward adaptive reasoning that scales compute to task difficulty, and that positioning usually predicts which feels better on your codebase.
Which is cheaper, Gemini 2.5 Pro or GPT-5.1?
They are priced almost identically, so cost will not decide between them.
Which has the bigger context window?
Gemini 2.5 Pro — 1M vs 400K, about 2.5× larger. Useful only if the model actually reasons over the full window, which not all do.
Can I use both Gemini 2.5 Pro and GPT-5.1 together?
Yes — a multi-model platform like LumiChats gives you Gemini 2.5 Pro, GPT-5.1 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, Gemini 2.5 Pro or GPT-5.1?
GPT-5.1 — released November 13, 2025, about 6 months after Gemini 2.5 Pro.
Specifications and benchmarks reflect publicly reported figures as of June 2026 and may change as providers release updates. Always verify on your own workload.