Qwen 3.8 Max bills $2 per million input tokens and $6 per million output, and its cheapest reliable configuration is not the one the API seems to offer. Turning thinking off with reasoning_effort: "none" dropped our two-step arithmetic task from 4/4 correct to 1/6, while granting a hard budget of just 16 thinking tokens restored 6/6, averaging a fifth fewer output tokens than the default. Launch week produced loud capability claims and little to check them against: no model card, no public benchmark table, internal-only evals, which Hacker News was quick to flag. Billing behavior is different, because anyone with an API key can measure it. We measured qwen3.8-max on day one through the Synthorai gateway: every thinking control the surface accepts, the reasoning tax at each setting, the implicit cache's floor and build lag, the 1M-context claim, and what carries over from Qwen 3.7.
TL;DR
qwen3.8-max's seven reasoning_effort values collapse into four measured behaviors: off, a 4,096-token cap, a 16,384 cap, and unbounded.
thinking_budget is exact: request 16 tokens and the meter reads 16; the ceiling is 262,144.
With thinking off, 2-hop math fell to 1/6 correct; a 16-token budget scored 6/6 for less.
