ACP usage_update reports size: 65536 for deepseek/deepseek-v4-pro (should be ~1M) #30120

Summary

When OpenCode runs deepseek/deepseek-v4-pro over ACP, the usage_update notification reports size: 65536 (64 K). DeepSeek V4 Pro advertises a 1 M context window, so ACP clients render a misleadingly tight "ctx N / 64 K" indicator and warn the user about running out of context far too early.

Same pattern as #16709 (MiMo-V2-Flash-TEE reporting 32 K instead of 262 K) and #20317 (GitHub Copilot Claude models reporting wrong context limits) — likely a stale or wrong entry in the model registry, but for a different provider/model pair.

Repro

OpenCode 1.15.11 launched with --model deepseek/deepseek-v4-pro:

```
[15:23:38.714] usage_update raw={"sessionUpdate":"usage_update","used":14388,"size":65536,"cost":{"amount":0.005717878,"currency":"USD"}}
```

size: 65536 is exactly 64 K — looks like a default/stale value rather than the model's real window.

Expected

size should reflect DeepSeek V4 Pro's actual context capacity (~1 M tokens). Whatever the canonical source is (models.dev entry, hard-coded provider config, etc.) needs the correct value.

Why this matters for clients

ACP clients (HAPI, Zed, Fabriqa, …) use size directly as the context-window denominator in their status bars. Reporting 64 K when the model can handle 1 M means:

• the "% used" indicator pegs near 100% on prompts that are nowhere near the real ceiling,
• compact/handoff warnings fire prematurely,
• users may waste tokens trying to shrink prompts that were already fine.

Related

• MiMo-V2-Flash-TEE has the wrong context window size? #16709 — MiMo-V2-Flash-TEE has the wrong context window size? (closed; same shape, different model)
• fix: GitHub Copilot Claude models have wrong context limits and missing thinking variants #20317 — fix: GitHub Copilot Claude models have wrong context limits and missing thinking variants (closed; same shape, different provider)

Environment

• OpenCode version: 1.15.11
• Model: deepseek/deepseek-v4-pro
• Provider: DeepSeek
• Client: HAPI (https://github.com/tiann/hapi)