GPT-5.2 vs o3
GPT-5.2 (released 2025-12-10) and o3 (released 2025-04-16) are both OpenAI reasoning models, but they're built for different jobs. GPT-5.2 doubles o3's context window (400K vs 200K tokens) and adds an xhigh reasoning effort tier; o3 is cheaper on output tokens and has a known knowledge cutoff (2024-06-30) that GPT-5.2's record doesn't specify. Both are available on OpenKey with one API key and a flat 3% fee over provider list price.
Spec vs spec
| Spec | GPT-5.2 | o3 |
|---|---|---|
| Context window | 400K | 200K |
| Max output | 128K | 100K |
| Input modalities | file, image, text | image, text, file |
| Output modalities | text | text |
| Knowledge cutoff | — | Jun 30, 2024 |
| Released | Dec 10, 2025 | Apr 16, 2025 |
| Reasoning | optional | optional |
Pricing
Per 1M tokens. Provider price plus the flat 3% fee — the sum is what you pay.
openai/gpt-5.2
Input · 1M tokens
$1.75 + 3%$1.80
Output · 1M tokens
$14.00 + 3%$14.42
Cache read · 1M tokens
$0.175 + 3%$0.180
FEE — FLAT, EVERY MODEL3%
openai/o3
Input · 1M tokens
$2.00 + 3%$2.06
Output · 1M tokens
$8.00 + 3%$8.24
Cache read · 1M tokens
$0.500 + 3%$0.515
FEE — FLAT, EVERY MODEL3%
One workload, priced on both
10M input + 2M output tokens at each model's price, flat 3% fee included.
openai/gpt-5.2
$46.87
$45.50 provider + 3%
openai/o3Cheaper
$37.08
$36.00 provider + 3%
Benchmarks
Design Arena categories where both models have results. Higher Elo and lower rank win.
| GPT-5.2 | o3 | |||
|---|---|---|---|---|
| Category | Elo | Rank | Elo | Rank |
| Code | 1219 | #42 | 1069 | #85 |
| Data viz | 1245 | #31 | 1200 | #49 |
| Game dev | 1260 | #29 | 1100 | #78 |
| UI components | 1243 | #32 | 1073 | #79 |
| Websites | 1237 | #34 | 1079 | #87 |
Head-to-head preference voting. How we filter and rank
Pricing math on a real workload
Provider list price for GPT-5.2 is $1.75/M input and $14.00/M output; OpenKey adds 3%, landing at $1.8025/M and $14.42/M. o3 lists at $2.00/M input and $8.00/M output, or $2.06/M and $8.24/M on OpenKey. Run the numbers on 10M input tokens + 2M output tokens: GPT-5.2 costs $45.50, o3 costs $36.00. GPT-5.2's input price is actually 12% cheaper than o3's (the input price ratio is 0.88), but its completion price is 1.75x higher, and completion cost dominates this workload. If your app is output-heavy (long generations, verbose agent traces), o3 is the cheaper call. If it's input-heavy (large context dumps, RAG), GPT-5.2's lower input price closes the gap.
Coding and agent benchmarks
Design Arena data covers five overlapping categories, and GPT-5.2 wins all of them. Codecategories: GPT-5.2 rank 42 (elo 1219, 50.2% win rate) vs o3 rank 85 (elo 1069, 51.9% win rate) — note o3 actually has a slightly higher win rate but a much lower elo and worse rank, meaning it's winning against weaker opponents. Dataviz: GPT-5.2 rank 31 vs o3 rank 49. Gamedev: GPT-5.2 rank 29 vs o3 rank 78. UI component: rank 32 vs 79. Website: rank 34 vs 87. GPT-5.2 also has agent-specific benchmarks (Android native, full-stack, Godot, mobile, web apps) that o3 has no recorded scores for at all — GPT-5.2 is the newer, more agent-tested model by a wide margin.
Context and long-document work
GPT-5.2 gives you 400,000 tokens of context against o3's 200,000 — exactly double. Max completion length is also larger: 128,000 tokens vs o3's 100,000. If you're processing full codebases, long contracts, or multi-document RAG pipelines in a single call, GPT-5.2 is the only one of the two that fits without chunking. o3's smaller window is still workable for most single-document tasks, but anything approaching book-length input needs GPT-5.2.
Reasoning controls and caching
GPT-5.2 exposes five reasoning efforts (none, low, medium, high, xhigh) with medium as default, giving you a dial between latency and depth. o3's record shows reasoning support but no effort tiers or default listed, so you get less control over the speed/quality tradeoff. Cached input reads are cheaper on both: GPT-5.2 at $0.175/M provider price, o3 at $0.50/M — GPT-5.2's cache is roughly 2.9x cheaper per token, which matters for repeated-context agent loops.
Which model for which job
| Use case | Pick | Why |
|---|---|---|
| Long-document analysis (contracts, codebases) | GPT-5.2 | 400K context vs o3's 200K — double the room before you need to chunk |
| High-volume short-answer API calls | o3 | $8.24/M output on OpenKey vs $14.42/M — cheaper when output tokens dominate cost |
| Coding agents / full-stack app generation | GPT-5.2 | Ranks 21st and 42nd in agent/codecategories benchmarks with scores o3 doesn't have |
| Repeated-context agent loops with caching | GPT-5.2 | Cache read at $0.175/M provider price vs o3's $0.50/M |
| Budget-conscious workload with light input, heavy output | o3 | 10M-in/2M-out benchmark workload costs $36.00 vs GPT-5.2's $45.50 |
| UI/dataviz/gamedev generation tasks | GPT-5.2 | Beats o3 in every shared Design Arena category (dataviz rank 31 vs 49, gamedev 29 vs 78) |
Questions
- Which is cheaper for a typical workload?
- Depends on the mix. For 10M input + 2M output tokens, o3 costs $36.00 on OpenKey versus GPT-5.2's $45.50 — o3 wins because its output price is lower. But GPT-5.2's input price is 12% cheaper (ratio 0.88), so input-heavy workloads narrow or flip that gap.
- How much bigger is GPT-5.2's context window?
- GPT-5.2 supports 400,000 tokens of context, exactly double o3's 200,000 — a context ratio of 2.0. Max completion length is also larger: 128,000 tokens versus 100,000 for o3.
- Does GPT-5.2 actually beat o3 on coding benchmarks?
- Yes, on every shared Design Arena category. Codecategories: rank 42 vs rank 85. Gamedev: rank 29 vs rank 78. UI component: rank 32 vs rank 79. Website: rank 34 vs rank 87. GPT-5.2 also has agent benchmarks (Android native, full-stack, web apps) with no o3 equivalent recorded.
- Can I use both models through one API key?
- Yes — both GPT-5.2 and o3 run on OpenKey with a single API key, and pricing is the provider's list price plus a flat 3% fee (e.g., GPT-5.2's $14.00/M provider output price becomes $14.42/M on OpenKey).