Google I/O 2026

Inference Stopped Being the Cheap Half

原演讲者: Google TPU software team, Google · Google

来源已核验演讲日期待核实presentation37:44EN2 分钟阅读

Performance gains that require rewriting the serving layer are migration projects with a performance argument attached — which is why the commitment that the application layer never changes decides whether specialised inference hardware is adoptable at all.

The observation this session builds on is that inference stopped being the cheap half.

Thinking models consume large numbers of tokens while reasoning through a problem (1:44), which means the compute profile of serving a model no longer resembles the profile that shaped serving infrastructure. Training and inference are described as two distinct phases with genuinely different requirements (1:48), and the response is to stop treating them with one general-purpose system (2:38).

Where the difficulty actually lives

The framing that transfers past any particular hardware is their account of what makes inference hard.

The difficult problems are memory management, scheduling and hardware utilisation, plus abstracting all of it away from whoever is building on top (4:19). Not matrix arithmetic. The chip does the arithmetic; the surrounding system decides whether the chip is busy.

The concrete bottleneck they identify is the key-value cache. As context lengths grow and concurrency rises, managing that cache becomes one of the biggest constraints on inference (4:38). This is the unglamorous centre of serving economics: a system that recomputes cached attention state is doing expensive work twice, and one that keeps too much of it runs out of memory under load.

The optimisation follows directly — reuse what was already calculated rather than recalculating it (5:13) — and it matters more as conversations get longer, which is exactly the direction usage is moving.

Batching, and why the old approach broke

The scheduling change is small to state and large in effect.

Static request-level batching groups a fixed set of requests and processes them together. It assumes they take similar amounts of time. Generation does not work that way: requests finish at wildly different points depending on how much output each produces, so a static batch is held hostage by its slowest member while finished slots sit idle.

Continuous batching (5:32) admits new work as slots free. The reason this became necessary is a consequence of reasoning models — variable-length output is no longer an edge case, it is the normal case, and infrastructure calibrated to uniform requests wastes most of its capacity.

The claim that determines whether any of it is adoptable

The commitment that matters commercially is stated almost in passing: as a developer you never have to rewrite your application layer or serving stack (6:43).

That is the whole argument for specialised hardware. Performance gains that require rewriting the serving layer are not gains — they are a migration project with a performance argument attached, and most organisations decline. Gains available behind an unchanged interface are adoptable by teams who never think about the hardware at all.

The corresponding detail is that this work happens in the open, including contributions arriving from outside — a research group's speculative decoding technique is cited as an example (14:54). For infrastructure whose value depends on being the default path, that openness is strategy rather than generosity.

演讲章节

关键要点

  1. 01

    Thinking models consume large numbers of tokens while reasoning, which changes the compute profile serving infrastructure was built for. 1:44

  2. 02

    The hard problems in inference are memory management, scheduling and utilisation rather than arithmetic — the chip computes, the system decides whether it is busy. 4:19

  3. 03

    Key-value cache management becomes one of the biggest bottlenecks as context lengths grow and concurrency rises. 4:38

  4. 04

    Continuous batching replaces static request-level batches because variable-length output stopped being an edge case. 5:32

  5. 05

    Their commercially decisive commitment is that developers never rewrite the application layer or serving stack to get the gains. 6:43

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