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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsTo version an API without breaking existing clients, preserve the existing contract whenever possible: add capabilities without changing what current requests and responses mean. If a change requires clients to update, publish a new major contract, run it alongside the old one during migration, and give consumers clear upgrade instructions and a retirement plan. A version label alone does not guarantee compatibility.
What does “breaking” mean for an API?
A change is breaking when a client must change its implementation to keep working. That can mean more than a changed schema: request and response shapes, error contracts, and externally visible behavior are all part of the contract. Microsoft Graph defines breaking changes in these terms, including changes to the API contract and behavior (Microsoft Graph versioning and support).
Start by documenting what clients can rely on: routes and methods, parameters, headers, field names and types, errors, and behavior. Also decide whether consumers are expected to tolerate unknown response fields, enum values, or derived types. The right compatibility promise depends partly on the clients you support.
Common changes that can break clients
- Removing or renaming an operation, parameter, field, or header that clients use.
- Changing an existing field’s type or meaning.
- Adding a required request field or changing validation so previously valid requests fail.
- Changing response behavior, error codes, or error formats in a way that clients depend on.
- Adding response fields when strict decoders or generated clients reject unknown fields.
Microsoft’s REST guidance notes that organizations may define compatibility differently, including whether adding a JSON response field is considered safe. Do not assume every client ecosystem handles additive fields the same way; state the rule and test representative clients (Microsoft REST API Guidelines).
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Prefer compatible, additive changes
When you can meet the need without changing existing meanings or required inputs, extend the current API. Examples include adding an optional capability or a new operation while preserving the behavior of existing ones. This lets deployed clients continue using the contract they already understand.
“Additive” is not automatically synonymous with “safe.” A new response property may be harmless to a tolerant client and fatal to one that rejects unknown properties. A new enum value or derived type can create a similar problem if a client assumes the set is closed. Define what old clients must tolerate, then check that promise against generated clients and strict decoders before release.
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Choose a version-selection scheme clients can use consistently
Version selection should make the chosen contract clear to clients and straightforward for your team to route, document, deploy, and observe. Microsoft REST guidance describes both a version in the request path and a query parameter; it emphasizes consistency when services share an endpoint. Google Cloud Endpoints recommends putting the major version in the base path (Google Cloud Endpoints: Versioning an API).
| Approach | What the sources describe | Decision to make |
|---|---|---|
Path, such as /v2/ |
Microsoft REST guidance allows a version in the request path; Google Cloud Endpoints recommends a major version in the base path. | Can your services use a consistent path convention, and is the version visible in documentation and generated clients? |
Query parameter, such as ?api-version=2 |
Microsoft REST guidance allows a version query parameter. | Does your routing, caching, proxying, and client tooling handle the parameter reliably? |
These are documented options, not a universal winner. Pick a convention and apply it consistently across services that share an endpoint. Consider how each choice affects routing, caches and proxies, generated clients, and the operational burden of supporting more than one contract.
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Version numbers are useful only when their meaning is documented and consistently applied. Google Cloud Endpoints advises increasing the minor version for compatible changes and the major version when a change breaks client code. A Google Cloud product manager likewise described Google’s API versioning as following general semantic-versioning principles, with major changes for backward-incompatible changes and minor changes for compatible ones (Google Cloud Endpoints versioning guidance; Google Cloud Blog: Versioning APIs at Google).
That is a convention, not a guarantee or universal specification. Explain whether your version represents a major contract, a release, or both; do not imply that a number makes a breaking change safe. Google Cloud Endpoints, for example, documents release numbering in the OpenAPI info.version separately from the major version in the base path.
Roll out an incompatible change without forcing a synchronized upgrade
When a change truly requires clients to update, introduce a new major contract and keep the previous one available while consumers migrate. Microsoft guidance calls for a clear upgrade path and deprecation plan; Google Cloud Endpoints documents concurrent major versions as part of its platform-specific lifecycle guidance (Microsoft Graph versioning and support; Google Cloud Endpoints: Versioning an API).
- Define both contracts. Publish what each version accepts and returns, including errors and behavior, and identify exactly what changed.
- Provide an upgrade path. Explain the replacement behavior and show how clients move from the old contract to the new one.
- Operate both versions deliberately. Decide how each is routed, tested, monitored, and supported. Google’s guidance describes one approach—implementing concurrent major versions in one backend—but this is specific to its platform workflow, not a requirement for every API.
- Make the migration trackable. Publish a change log and migration instructions. Where possible, measure which clients still call the old version and use that information to target communication.
- Announce deprecation and retirement clearly. Publish support status and the planned retirement date under your own policy, allowing for the number of independently deployed consumers and the cost of updating them.
- Retire through the announced process. Confirm clients have a documented path forward, then publish the old version’s final status.
Keep preview policies distinct from production promises. Microsoft Graph warns that its beta APIs can change and are not supported for production use (Microsoft Graph versioning and support).
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Set a retirement window that fits your service
There is no general retirement period established here that applies to every API. Microsoft Graph says it declares a version deprecated at least 24 months before retirement; that is Microsoft Graph policy, not an industry-wide minimum. Set and publish a support timeline that reflects your own commitments and customer impact, and make the dates and status easy to find (Microsoft Graph versioning and support).
Quick Recap
A practical compatibility check before release
- Have you recorded the contract clients actually depend on, including errors and observable behavior?
- Could an existing client fail because a field, operation, parameter, or meaning changed?
- Have you tested additions against clients that may reject unknown fields, enum members, or types?
- Can consumers see which version they are calling and which contract it selects?
- If the change is incompatible, are the old and new contracts documented and supported during migration?
- Are upgrade instructions, deprecation status, monitoring, and the retirement date explicit?
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