Tokens were only counted post-hoc (onFinish) and the header badge updated only on
chat open/switch; reasoning wasn't requested or shown. Now a counter ticks LIVE
during generation and surfaces reasoning ("thinking") tokens separately, like
Claude Code's `Thinking… · N tokens`.
Architecture (AI SDK v6): no provider gives exact per-token usage mid-stream, so
the live number is a cheap client estimate (chars/≈4) reconciled to AUTHORITATIVE
provider usage at step boundaries and turn end. The useChat per-delta re-render is
the existing realtime engine.
- server: `chatStreamMetadata` now also forwards usage on `finish-step` + `finish`;
`sendReasoning: true`; persisted `metadata.usage` carries `reasoningTokens`
(normalized from `outputTokenDetails` or the deprecated field).
- client: pure `count-stream-tokens` (estimateTokens / liveTurnTokens, prefers
authoritative usage else estimate); `Thinking… · N tokens` in the typing
indicator; collapsible "Thinking" reasoning block; throttled (~8 Hz) live
turn-token header badge; `reasoningTokens` in types + Markdown export.
Review fixes folded in:
- v6 `finish-step.usage` is PER-STEP, not cumulative — the server now ACCUMULATES
a running sum (new pure `accumulateStepUsage`) and sends the cumulative, which
converges to `finish.totalUsage`, so the live counter never jumps DOWN on a
multi-step agent turn.
- reasoning double-count: the authoritative turn-total is attributed to a block
ONLY for a single-reasoning-part (one-step) turn; multi-step blocks each show
their own estimate (the authoritative total stays in the header).
- no "0" badge flash at turn start (require live > 0, else show context size).
- comment refreshed (finish-step trigger).
Tests: server `accumulateStepUsage` + updated `chatStreamMetadata` (34 in the
suite); client pure-fn tests. Both tsc clean; 162 client ai-chat + the ai-chat
server suite pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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