diff --git a/data/deprecations/17-9-ast-da-dast-devtools-api-timeout-env-change.yml b/data/deprecations/17-9-ast-da-dast-devtools-api-timeout-env-change.yml
new file mode 100644
index 0000000000000000000000000000000000000000..f61836903ad94980cfa1b91a23191b35927c02cf
--- /dev/null
+++ b/data/deprecations/17-9-ast-da-dast-devtools-api-timeout-env-change.yml
@@ -0,0 +1,20 @@
+- title: "DAST `dast_devtools_api_timeout` will have a lower default value"
+  removal_milestone: "18.0"
+  announcement_milestone: "17.9"
+  breaking_change: true
+  window: 1
+  reporter: DavidNelsonGL
+  stage: application security testing
+  issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/517254
+  impact: low
+  scope: project
+  resolution_role: Developer
+  manual_task: false
+  body: |  # (required) Don't change this line.
+    The `DAST_DEVTOOLS_API_TIMEOUT` environment variable determines how long a DAST scan waits for a response from the browser. Before GitLab 18.0, the variable has a static value of 45 seconds. After GitLab 18.0, `DAST_DEVTOOLS_API_TIMEOUT` environment variable has a dynamic value, which is calculated based on other timeout configurations.
+    In most cases, the 45-second value was higher than the timeout value of many scanner functions. The dynamically calculated value makes the `DAST_DEVTOOLS_API_TIMEOUT` variable more useful by increasing the number of cases it applies to.
+  end_of_support_milestone:
+  tiers: [Ultimate]
+  documentation_url: https://docs.gitlab.com/ee/user/application_security/dast/browser/configuration/variables.html
+  image_url:
+  video_url:
diff --git a/doc/update/breaking_windows.md b/doc/update/breaking_windows.md
index 988bf423af92e4fd4deb6ff34002b8af26bf0095..342569785b9ba895b809c242a72da46e14cdefac 100644
--- a/doc/update/breaking_windows.md
+++ b/doc/update/breaking_windows.md
@@ -48,6 +48,7 @@ This window takes place on April 21 - 23, 2025 from 09:00 UTC to 22:00 UTC.
 | [Dependency Scanning for JavaScript vendored libraries](https://gitlab.com/gitlab-org/gitlab/-/issues/501308) | Low | Application_security_testing | Project |
 | [Dependency Scanning upgrades to the GitLab SBOM Vulnerability Scanner](https://gitlab.com/gitlab-org/gitlab/-/issues/501308) | High | Application_security_testing | Project |
 | [Resolve a vulnerability for Dependency Scanning on Yarn projects](https://gitlab.com/gitlab-org/gitlab/-/issues/501308) | Low | Application_security_testing | Project |
+| [DAST `dast_devtools_api_timeout` will have a lower default value](https://gitlab.com/gitlab-org/gitlab/-/issues/517254) | Low | Application security testing | Project |
 | [API Discovery will use branch pipelines by default](https://gitlab.com/gitlab-org/gitlab/-/issues/515487) | Low | Application_security_testing | Project |
 | [Container Scanning default severity threshold set to `medium`](https://gitlab.com/gitlab-org/gitlab/-/issues/515358) | Low | Application security testing | Project |
 | [Subscription related API endpoints in the public API are deprecated](https://gitlab.com/gitlab-org/gitlab/-/issues/515371#note_2319368251) | Low | Fulfillment | Instance |
diff --git a/doc/update/deprecations.md b/doc/update/deprecations.md
index 43fa9b6f75acc2e8b4abfcc096cc3e64ae9847bf..5681ceae15217148dc32d7711b8f80aea601e317 100644
--- a/doc/update/deprecations.md
+++ b/doc/update/deprecations.md
@@ -597,6 +597,23 @@ To continue showing these findings, you must configure the `CS_SEVERITY_THRESHOL
 
 <div class="deprecation breaking-change" data-milestone="18.0">
 
+### DAST `dast_devtools_api_timeout` will have a lower default value
+
+<div class="deprecation-notes">
+
+- Announced in GitLab <span class="milestone">17.9</span>
+- Removal in GitLab <span class="milestone">18.0</span> ([breaking change](https://docs.gitlab.com/ee/update/terminology.html#breaking-change))
+- To discuss this change or learn more, see the [deprecation issue](https://gitlab.com/gitlab-org/gitlab/-/issues/517254).
+
+</div>
+
+The `DAST_DEVTOOLS_API_TIMEOUT` environment variable determines how long a DAST scan waits for a response from the browser. Before GitLab 18.0, the variable has a static value of 45 seconds. After GitLab 18.0, `DAST_DEVTOOLS_API_TIMEOUT` environment variable has a dynamic value, which is calculated based on other timeout configurations.
+In most cases, the 45-second value was higher than the timeout value of many scanner functions. The dynamically calculated value makes the `DAST_DEVTOOLS_API_TIMEOUT` variable more useful by increasing the number of cases it applies to.
+
+</div>
+
+<div class="deprecation breaking-change" data-milestone="18.0">
+
 ### Dependency Proxy token scope enforcement
 
 <div class="deprecation-notes">