LongCat-Flash-Thinking: API Alias Upgrade, Automatic Routing, and Service-Retirement Boundaries

One-sentence takeaway

Code that called LongCat-Flash-Thinking historically has been automatically routed to 2601 since 2026-03-12, and both old models were retired on 2026-05-29, so every evaluation must record the call date and actual version.

Test environment

• Environment type: Production-service change records from the official LongCat API Platform, not a quality benchmark.

• Observation targets: API model aliases, automatic-routing rules, open-source/platform launch dates, and service lifecycle.

• Key versions: The first-generation LongCat-Flash-Thinking, the upgraded LongCat-Flash-Thinking-2601, and the later LongCat-2.0-Preview and LongCat-2.0.

Input/configuration

When reviewing historical results, record at minimum: request time (UTC+8), the model string in the request, provider/endpoint, whether thinking or tools were used, and the weights or platform version. Recording only model=LongCat-Flash-Thinking is not enough to determine the actual version.

Results data

Conclusions

• Suitable for: Version labeling for historical evaluations and cost records, API migration, or determining which LongCat snapshot a piece of old code actually evaluated.

• Unsuitable for: Treating a changelog as evidence of quality, latency, or tool success-rate testing.

• Most important reproduction fields: Time, alias, and the server-side route; local open-source weights should instead record the exact repository/commit.

Limitations

• The changelog provides no complete quality, throughput, pricing, or error-rate data for any version.

• “Automatic routing to the latest version” describes platform behavior, but this page provides no response-metadata example; it cannot support guessing that every gateway echoes the actual version.

• After retirement, API-only reproduction may be blocked by service status; locally saved weights and environments, or an official request for legacy-version access, are needed.

Reproduction steps

1. Split historical experiments at 2026-03-12 20:00 (UTC+8) and save request logs separately.

2. Retain the model string, endpoint, response time, tool/thinking switches, and complete input/output for every record.

3. Label results for the old alias before retirement as “platform-routed results”; do not label them directly as results from the 2601 local weights.

4. If migrating to LongCat-2.0, establish a new baseline rather than concatenating post-migration scores longitudinally with the old model.

Original evidence and data

• The changelog explicitly records that, beginning on 2026-03-12, the old alias was automatically routed to LongCat-Flash-Thinking-2601.

• The 2026-05-29 retirement list includes both the first-generation Flash-Thinking and 2601.

• The 2026-01-14 entry describes the upgraded version as a 560B MoE and mentions a 60+ tool dependency graph, noise robustness, and an advanced deep-thinking mode.

Applicability boundaries

This material can establish only service-lifecycle and routing facts. It cannot establish the specific improvement of 2601 over the first generation or prove task equivalence after migration to LongCat-2.0.

Source excerpt or observation (short quote for compliance only)

The key changelog statement is that requests using the old alias are automatically routed to the latest LongCat-Flash-Thinking-2601; the rule has a clearly specified effective time.