diff --git a/guix-data-service/web/compare/controller.scm b/guix-data-service/web/compare/controller.scm
index c992186..e6ea566 100644
--- a/guix-data-service/web/compare/controller.scm
+++ b/guix-data-service/web/compare/controller.scm
@@ -26,6 +26,8 @@
   #:use-module (texinfo html)
   #:use-module (texinfo plain-text)
   #:use-module (json)
+  #:use-module (fibers)
+  #:use-module (knots promise)
   #:use-module (knots parallelism)
   #:use-module (knots resource-pool)
   #:use-module (guix-data-service utils)
@@ -307,97 +309,134 @@
                 (version-changes
                  (package-data-version-changes base-packages-vhash
                                                target-packages-vhash)))
-            (fibers-let ((lint-warnings-data
-                       (with-resource-from-pool (connection-pool) conn
-                         (group-list-by-first-n-fields
-                          2
-                          (lint-warning-differences-data conn
-                                                         base-revision-id
-                                                         target-revision-id
-                                                         locale))))
-                      (channel-news-data
-                       (with-resource-from-pool (connection-pool) conn
-                         (channel-news-differences-data conn
+            (let ((lint-warnings-data-promise
+                   (fibers-delay
+                    (lambda ()
+                      (with-resource-from-pool (connection-pool) conn
+                        (group-list-by-first-n-fields
+                         2
+                         (lint-warning-differences-data conn
                                                         base-revision-id
-                                                        target-revision-id))))
+                                                        target-revision-id
+                                                        locale))))))
+                  (channel-news-data-promise
+                   (fibers-delay
+                    (lambda ()
+                      (with-resource-from-pool (connection-pool) conn
+                        (channel-news-differences-data conn
+                                                       base-revision-id
+                                                       target-revision-id))))))
+              ;; TODO Make this neater
+              (spawn-fiber
+               (lambda ()
+                 (fibers-force lint-warnings-data-promise))
+               #:parallel? #t)
+              (spawn-fiber
+               (lambda ()
+                 (fibers-force channel-news-data-promise))
+               #:parallel? #t)
+
               (case (most-appropriate-mime-type
                      '(application/json text/html)
                      mime-types)
                 ((application/json)
                  (render-json
-                  `((base-commit    . ,(assq-ref query-parameters 'base_commit))
-                    (target-commit  . ,(assq-ref query-parameters 'target_commit))
-                    (channel-news . ,(list->vector
+                  (lambda (port)
+                    (scm-alist->streaming-json
+                     `((base-commit   . ,(assq-ref query-parameters 'base_commit))
+                       (target-commit . ,(assq-ref query-parameters 'target_commit))
+                       (channel-news
+                        .
+                        ,(lambda (port)
+                           (list->json-array
+                            (match-lambda
+                              ((commit tag title_text body_text change)
+                               `(,@(if (null? commit)
+                                       '()
+                                       `((commit . ,commit)))
+                                 ,@(if (null? tag)
+                                       '()
+                                       `((tag . ,tag)))
+                                 (title-text
+                                  . ,(map
+                                      (match-lambda
+                                        ((lang . text)
+                                         (cons
+                                          lang
+                                          (texinfo->variants-alist text))))
+                                      title_text))
+                                 (body-text
+                                  . ,(map
+                                      (match-lambda
+                                        ((lang . text)
+                                         (cons
+                                          lang
+                                          (texinfo->variants-alist text))))
+                                      body_text))
+                                 (change . ,change))))
+                            (fibers-force channel-news-data-promise)
+                            port)))
+                       (new-packages
+                        .
+                        ,(lambda (port)
+                           (list->json-array
+                            identity
+                            new-packages
+                            port)))
+                       (removed-packages
+                        .
+                        ,(lambda (port)
+                           (list->json-array
+                            identity
+                            removed-packages
+                            port)))
+                       (version-changes
+                        . ,(lambda (port)
+                             (list->json-array
+                              (match-lambda
+                                ((name data ...)
+                                 `((name . ,name)
+                                   ,@data)))
+                              version-changes
+                              port)))
+                       (lint_warnings
+                        .
+                        ,(lambda (port)
+                           (list->json-array
+                            (match-lambda
+                              (((package-name package-version)
+                                . warnings)
+
+                               `((package
+                                   . ((name . ,package-name)
+                                      (version . ,package-version)))
+                                 (warnings
+                                  . ,(list->vector
                                       (map
                                        (match-lambda
-                                         ((commit tag title_text body_text change)
-                                          `(,@(if (null? commit)
-                                                  '()
-                                                  `((commit . ,commit)))
-                                            ,@(if (null? tag)
-                                                  '()
-                                                  `((tag . ,tag)))
-                                            (title-text
-                                             . ,(map
-                                                 (match-lambda
-                                                   ((lang . text)
-                                                    (cons
-                                                     lang
-                                                     (texinfo->variants-alist text))))
-                                                 title_text))
-                                            (body-text
-                                             . ,(map
-                                                 (match-lambda
-                                                   ((lang . text)
-                                                    (cons
-                                                     lang
-                                                     (texinfo->variants-alist text))))
-                                                 body_text))
-                                            (change . ,change))))
-                                       channel-news-data)))
-                    (new-packages . ,(list->vector new-packages))
-                    (removed-packages . ,(list->vector removed-packages))
-                    (version-changes . ,(list->vector
-                                         (map
-                                          (match-lambda
-                                            ((name data ...)
-                                             `((name . ,name)
-                                               ,@data)))
-                                          version-changes)))
-                    (lint_warnings
-                     . ,(list->vector
-                         (map
-                          (match-lambda
-                            (((package-name package-version)
-                              . warnings)
+                                         ((lint-checker-name
+                                           message
+                                           lint-checker-description
+                                           lint-checker-network-dependent
+                                           file line column-number
+                                           change)
 
-                             `((package
-                                . ((name . ,package-name)
-                                   (version . ,package-version)))
-                               (warnings
-                                . ,(list->vector
-                                    (map
-                                     (match-lambda
-                                       ((lint-checker-name
-                                         message
-                                         lint-checker-description
-                                         lint-checker-network-dependent
-                                         file line column-number
-                                         change)
-
-                                        `((change  . ,change)
-                                          (checker
-                                           . ((name . ,lint-checker-name)
-                                              (description
-                                               . ,lint-checker-description)))
-                                          (message . ,message)
-                                          (location
-                                           . ((file   . ,file)
-                                              (line   . ,(string->number line))
-                                              (column . ,(string->number
-                                                          column-number)))))))
-                                     warnings))))))
-                          lint-warnings-data))))
+                                          `((change  . ,change)
+                                            (checker
+                                             . ((name . ,lint-checker-name)
+                                                (description
+                                                 . ,lint-checker-description)))
+                                            (message . ,message)
+                                            (location
+                                             . ((file   . ,file)
+                                                (line   . ,(string->number line))
+                                                (column . ,(string->number
+                                                            column-number)))))))
+                                       warnings))))))
+                            (fibers-force lint-warnings-data-promise)
+                            port))))
+                     port))
+                  #:stream? #t
                   #:extra-headers http-headers-for-unchanging-content))
                 (else
                  (fibers-let ((lint-warnings-locale-options
@@ -422,9 +461,9 @@
                                     new-packages
                                     removed-packages
                                     version-changes
-                                    lint-warnings-data
+                                    (fibers-force lint-warnings-data-promise)
                                     lint-warnings-locale-options
-                                    channel-news-data)
+                                    (fibers-force channel-news-data-promise))
                     #:extra-headers http-headers-for-unchanging-content))))))))))
 
 (define (render-compare-by-datetime mime-types