Version pinning: what a fixed identifier covers
Pinning means naming an exact version so the same weights answer every call. It fixes that one thing precisely. The defaults around the call, the serving stack, and the date the pinned version itself is retired all keep moving, and most teams assume a pin covers more than it does. As of 2026-09-22.
| Fixed by the pin | Still moving |
|---|---|
| Which weights answer the call | Safety filters and prompt handling |
| The version identifier in your code | Resolution presets and rate limits |
| A row you can match to a dated notice | How long the pinned version is served |
| A cause you can rule out when output moves | The serving infrastructure behind it |
Inclusion rule. Distinctions drawn from how the programmable entries in this register describe versions. No entry here publishes a definition of pinning. Order. What the pin fixes first, then what it does not.
1A pin is a guarantee about the model, not the result
Output can still move under a pinned version, because much of what shapes a result lives outside the version identifier. What the pin buys is the ability to rule out the largest cause when something changes.
That is worth a great deal during a long production. Knowing the weights did not move turns an investigation into a short list instead of an open question.
2Every pin expires
A pinned version is eventually retired, so pinning buys a known amount of time rather than permanence. The useful follow-up question is how much notice the vendor gives and whether the figure is published anywhere.
Treating a pin as permanent is how a production discovers a retirement on the day it takes effect. Treating it as a lease with an unknown end is closer to right.
3Most products in this register have nothing to pin
An application presenting house tier names rather than version identifiers offers no pin at all. The engine can be replaced between one session and the next with the interface looking identical.
That is the common case here, and it means version stability is unavailable at any price on most of these entries. The default tier column records which ones name anything specific.
A definition rather than a dated entry: no line above is a vendor statement. Where this word turns up in a real notice, the wording and the date are on the longer explainer on pinning. Nearby terms: Model identifier, Model card, Changelog.