deepseek-chat and deepseek-reasoner Are Gone — What to Fix Right Now

TL;DR: The deepseek-chat and deepseek-reasoner API aliases retired at 15:59 UTC today — if your integration is broken right now, that's why. Migrate to deepseek-v4-flash with one non-obvious fix.

DeepSeek's backward-compatibility shim for deepseek-chat and deepseek-reasoner expired at 15:59 UTC on July 24. Both aliases had been pointing at deepseek-v4-flash under the hood since the V4 line shipped in April, kept alive purely for existing integrations. That shim is now gone.

The one-line fix

# Before
model = "deepseek-chat"     # or "deepseek-reasoner"

# After
model = "deepseek-v4-flash" # non-thinking path (see below)
# or
model = "deepseek-v4-pro"   # higher capability

The non-obvious catch: thinking mode

deepseek-v4-flash defaults to thinking enabled. If you swap deepseek-chat → deepseek-v4-flash without disabling it, you'll get reasoning output you never asked for: more tokens, higher latency, a bigger bill, and different downstream behavior in any system that parsed the old format.

To match the previous deepseek-chat behavior:

# OpenAI-compatible client
response = client.chat.completions.create(
    model="deepseek-v4-flash",
    extra_body={"thinking_enabled": False},   # suppress reasoning mode
    messages=[...]
)

Why it matters: If you route through OpenRouter, Together, or a local proxy that aliased deepseek-chat, check whether your routing layer failed hard or soft — and whether thinking_enabled passes through to the underlying model.

Sources: DeepSeek API changelog · Migration guide — Digital Applied · Developers Digest: migrate to V4